Preparation of phenols



Dec- 18, 1951 v. MOLINARI ET A1. 2,578,823

PREPARATION oF PHENoLs Filed sept. a, 1948 2 SHEETSTSEET 1 ATTORN EY R l l 1 l l l E wpwublm.. wcwncum Edoom x Mm Wdu/ Hmmm A OAH 4 u uwm Evom. n@ w d W mmc t n0 M. n e EOA .mn 32x05 Ldbjm k ne 00 M VMG. AMA A ut r 2 r Z mor .Ev n am e I mn V a o u V .L L E Bcd o A MB .1. c RY d u m C R vl/'EB 2 Y .SP 5. T vH /44 Z m S w 7u n N m u n. w H m C 2 d E L m e .@Bm 2m .1B M, w... l Lubdm A 1 I f N r. umddu f 6 k m u ,m L; 1 r T m 0 z n n A M 93m EN Y Tm W e Lomdcobdw n o F. 5 k e wl L BV w L .u l 0 or wm e e d w il @Z u Tv 3 e L W 2U r mm B a W Benzene 4 Oleum l: l Y

2 SHEETS-SHEET 2 V. MOLINARI ET AL PREPARATION OF PHENOLS Dec. 18, 1951 Filed Sept. 8. 1.948

INVENTORS VITTORIO MOLINA/Pl HERBERT G. AFFHOLTER l v I mv l ATTORNEY Paatfea o. is, 1,9451, t 2,578,823

n UNITED STATES PATENT y OFFICE PREPARATION OF PHEN OLS Vittorio Molinari, Plainfield, and Herbert G. Aifliolter, Bound Brook, N. J., assignors, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York Application September 8, 1948, Serial No. 48,292

1 Claim. (Cl. 260-628) 2 This invention relates to the preparation of Combining these equations gives the overall phenol from benzene by the sulfonation process. theoretical reaction expressed above. For the The classical sulfonation procedure consists in caustic fusion of the prior art is substituted the reacting benzene with sulfuric acid to form benhydrolysis yielding the sodium sulte which is zene sulfonic acid, neutralizing with milk of lime, .i utilized in preparing both the sulfonate and the filtering out the resulting calcium sulfate, and phenate for the hydrolysis step. In the phenate treating the filtrate with sodium carbonate to preparation, the lime plays the part of forming give sodium benzene sulfonate. The sodium benan insoluble sulte that precipitates to leave the zene sulfonate is dissolved ina melt or fusion sodium in the system for recycling.

of caustic soda and stirred for several hours, and Further improvements provided by the invena reaction conforming to the equation, tion reside in the steps, whereby a continuous process is made possible with the substantially CH5SO3Na+zNaoH-CsHONal-Naasos'l-Hzo overall result that benzene and sulfuric acid can ensues. The fusion DrOduCt 1S pured into Water be charged continuously at one end of the apand the phenol is released from the sodium params (with lime added in step 1V), and a Phenate. usually with sulfuric acid. While, stream of phenol is discharged at the other end. theoretically, two moles of caustic is suflicient for These Step improvements are ser our, in the dethe fusion, normal practice requires about three scriptum of the process that follows.

moles t maintain a fused liquid State and t0 A preferred form of this invention will be decontrol the foaming. For this reason, the process w scribed in greater detail with reference to the iS relatively `expensive. accompanying drawings, which comprise a purely According to the present invention, the caustic diagrammatic flow chart, illustrating in Fig. l soda reaction is replaced in a process which can the sulphonation and neutralization steps and in be expressed by the overall reaction equation Fig, 2 the hydrolysis and phenation steps in a CH6+x/H2S04+1/2Ca(0H),+1/2O= 3,-, continuous process according to the invention.

CaHaOH-ll@Gasoil-H I. Sulfonation of benzene The sulfonation of benzene by reacting with sulfuric acid as normally practiced is (l) feeding oleum (solution of 20% sulfur trioxide in 98% sulfuric acid) into liquid benzene at a rate such that the temperature is held between 70-8 C.

In operation the water of reaction dilutes the cost of phenol production is thus considerably lllfeurtcSlgngoteteenihatltslsthrog lessened.

. practice therefore to complete the utilization of The accomplishments of this Invent-'lon are the dilute sulfuric acid by (2) a second step of brought about by a combination of steps: passing through the mass vapors of benzene that Instead, therefore, of the consumption of two and more moles of caustic soda required by the classical process, the present invention utilizes onehalf mole of the much cheaper and prevalent lime converted to the sulte for each mole of phenol produced, andthe sulfuric acid consumption is also reduced to about one-half mole. The

I. Sulfonation of benzene, azeotropically distill the water present and so 40 concentrate the acid and enable the continua- CGHs'lHZSOlCI-ISSOIHl-HZO tion of the sulfonation of the benzene to con- II- Neutranzatmn t0 sodium, benzene Sulfonale tinuously decrease the free sulfuric acid content. C8H5SO3H+ 1/2Na2s03: When all but about l0 per cent of the sulfuric CSH5SOJN3+ r/zsOHJ/,Hzo acid has been reacted, diphenyl sulfone startsi5 forming according to the reaction; with the acid recovery,

III. Hydrolysis of a solution of sodium benzene This formation entails ajpprecable losses of bfth sulfonate 1n fused sodium phenate! l. benzene and sulfuric acid as well as constituting "0 an objectionable by-product for removal. CaH5SO3Na-l-C8H50Na-l-H2O:2C6H5OH+N3J2SO3 The present invention provides sulfonation at IV. Phenate formation from one-half the phenol, such mgh ylelds of bnzne'monosulfomc amd as to be free from obJectionable amounts of the CSHSOH+V2Na2SOS+V2CMOH 2= v by-products (benzene-disulfonic acid and di- CeHsONa-i- VgCaSOa-l-Ezg phenyl-sulfone) and in a condition for neutralifrom the top of the sulphonator.

zetion to the sodium salt without any purification s p. about by the inclusion-of a salt that acts as an inhibitor oi' the by-product formation. The salt is preferably sodium benzene sulphonate which does not import any ingredients requiring separation, but it can be any sodium salt engenderlng benzene sulfonate in the reaction such as the carbonate. sulfate. or sulii.

For the continuous process, illustrated by the now chart. the sulphonation step is preferably operated in three stages as shown on the left hand' Brleily this accomplishment is broughtl ants there is little tendency to form benzene- V ratio of the reactants and product in the discharged stream 5 is about 50 per cent benzenemonosulphonic acid with a content of about 29 per cent of free sulphuric acid and the remainder benzene. y

In the second stage, the stream of benzenesulphonic acid is fed from 5 to the next sulphonator 8. where the temperature ls kept between 150 and 170 C. Here-benzene vapors are supplied at 7 from benzene evaporator 8 and are bubbled upwardly (or countercurrenthr) through the down-flowing agitated liquid mass. This stage is operated to yield about 30v per cent of additional benzene sulfonic acid. The vapors of benzene, entrained water and Vacid are discharged at 9 The stream discharged at I0 passes to the next sulphonator Il.

Eer the third stage the concentration of ben- .of the sulphuric acid is very low, which condition enhances the -tendency to form diphenyl- 1 4 and I I. The water layer 20 is discharged to waste at 2|.

In the sulphonator II temperatures are maintainedconstant; this is necessary to a continuous process in order that ,the reaction conditions lremain uniform at all times.

n. Neutralization to the sodium salt As received from Vthe sulphonators at 22 the liquid benzene sulphonic aeid (with its added content of sodium benzene sulphonate) is sufciently free from contaminants so as to require no further puriflcatiom It is therefore fed directly to the neutralizer or sulphonate producer 23 'held Aat about 105 C.; the solid sodium sulphite also added via24 makes a viscous mass. and this is diluted at 25 by an incoming supply of mother liquor subsequently separated. In the neutralizer 23 the used caustic containing sodium benzene sulphonate from the scrubber I4 is added to the system via 26 compensating for sodium losses encountered in the process. In the l'neutralizer sulphur dioxide is driven oi at 21 and may be sent to an acid recovery plant.

The hot solution is discharged at 28 without concentration into a cooler '29 (150-50 C.) where the sodium benzene sulphonate precipitates in the form of iiaky crystals the mixture being fed via 30 to a continuous centrifuge 3I. The moist salt crystals discharged by the centrifuge are in t condition for the next step of the process.

The separated mother liquor is returned via 32 l to the neutralizar 23; and its recycling does not evidence any accumulation of impurities, even though the sodium sulphite 'fed to the neutralizer. is a by-product of the next step of the process. Sodium benzene sulphonate is discharged at 33, some passing Via 34 to the inlet 4 of sulphonator 3 and the remainder passing via 35 to the hydrolysis stage.

An alternative step of neutralization, and now found preferable, is feeding the sulfonation mass in a melted condition as it comes from the sulfonator directly to a kneader or the like containing solid sodium sulte obtained as a by-product in the succeeding hydrolysis step of the process;

charged as dry powder; the temperature is maintained suiciently high to avoid having any of sulphone. Even in this stage, however, the sodi-1 um salt carried in the stream is an effective inhibitor. `The third stage, also operated between 150 and 170 C., is a clean-up" operation for converting the remaining free sulphuric acid to less than 3%, whereby a final content of 93-to 94% of benzene-monosulphonic acid is obtained with no objectionable amounts of contaminants.

The vapors arising from the second and third sulphonators 6 and II are directed via 3, I2 and I3 through a caustic (NaOH) scrubber Il kept at 100 C. Here entrained sulphonic acid' is reacted to sodium sulphonate but without any condensationof benzene and water. The vapors, thus freed from the corrosive acid, then pass to a condenser |15 and a separator I6. They benzene layer I1 overows at I8 and iscarrled via I to the evaporator 8 that supplies the benzene vapor for the second and third sulphonators 6 the gas remaining in the powder, and the sulfur dioxide gas is returned to the sulfuric acid plant. The dry sodium benzene sulfonate as obtained is in condition for` the next step of hydrolysis.

A III. Hydrolysis In this step, shown in Fig. 2, free phenol is distilled by the passage of-dry steam through melted sodium phenate having the sodium benzene sulphonate salt dissolved therein. For the hydrolysis to proceed, the melt must be substantiallyA anhydrous and maintained liquid at the temperature of reaction. It is also essential that the temperature of hydrolysis be subject to close control; otherwise diphenyl oxide is apt to form, and this tendency' increases with a rise in the temperature above 370390 C.

vIt has-now been found that the hydrolysis can be most satisfactorily carried out in continuous operation by separating the'step of hydroysis from the step of melting. For this` reason concentrated sodium' phenate solution in excess and the ananas sodium benzene sulphonate powder is charged in a continuous ilow from 35 and 38 into a closed -melter 31 where they are lbrought to a temperature of 'about 300310 C. By this operation the sodium phenate is dehydrated and melted with the sulphonate dissolved therein. Consequently, a uniform anhydrous mass at the required temperature is continuously drawn from the melter at 38. In the melter 31 some phenol is released by hydrolysis and the water vapors carry it via 39 and 48 to the condenser. 'I'he molten mass delivered from the melter 31 at 4'2 is led to a hydrolyzer 48, provided with an agitator 44 and maintained at about 325 to 330 C., and dry steam is passed through it from 45. The steam emerging from the hydrolyzer at 48 carries the phenol and it passes with the vapors from 39 into 40 and thence into condenser 4|. The sodium phenate, in an excess necessary for maintaining a liquid melt, is drawn from the hydrolyzer 43 via 41 into a tank 48 where it is diluted to 30 Baume at 160 C. with phenolic water distilled in a subsequent operation of distillation of the crude phenol via 49 or with dilute phenates obtained in subsequent operation via -l). At this concentration anhydrous sodium sulfite precipitates. The sulphite crystals are discharged at 5| and separated in the continuous centrifuge 52 from the phenate solution. The sodium sulphite passes out via 53 and one-half of it goes via- 54 to 25 and thence the neutralizer 28 (Fig. 1) and the remainder goes via 55 to the phenate -producer 56. 'I'he phenate solution is returned via 51 and 58 from the centrifuge 52 to an evaporator 59 to be concentrated and returned to the cycle for the hydrolysis step. Water evaporated in this operation is conveniently used to supply the steam for the hydrolyzer 43 passing thence via 60 and 45; the phenate so concentrated is returned to the melter 31 via 6| and 36.

In this step an excess of phenate over the stoichiometric proportion for hydrolysis is maintained in order that the mass is liquid at all times. The melter functions as a cushion to maintain the high temperature in the hydrolyzer as well as to furnish an anhydrous stream oi' the salts.

IV. Phenate formation In the hydrolysis step previously described it is necessary to have a continuous supply of sodium phenate. Sodium phenate can be produced by reacting free phenol with caustic soda, and caustic soda can be produced by interaction of lime and sodium sulte. This reaction for obtaining caustic soda has been tried at various concentrations and temperatures for improving the yield, and it has been found that the best conversion to caustic soda (about 74%) occurred by reacting at 100 C. a concentration of sodium sulfite in water of only 5 per cent by weight and 20 per cent excess of the lime; at the same temperature and with the same excess of lime and a sulfite concentration, the conversion was reduced to less than 60%, and at 30% concentration the yield of caustic was less than 30 per cent. This means a highly diluted caustic soda solution requiring separation from the remaining lime and concentration for the hydrolysis. It has been found, however, that when phenol was included (according to the equation previously given), a concentrated solution (25%) of tlllate from'the melter 31 andthe hydrolyzer 48 sodium sulfite and only 5% excess of lime gave is passed via 39, 48 and 40 through the condenser 4 I, and the condensate goes via 62 to a separator 63 wherein free phenol collects in a bottom layer 84 while a saturated phenol-water layer 55 rests 'on top. 'I'he lower free phenol layer is drawn oil at 58 into a still 61 for distillation; it constitutes the output of product of the process, being discharged at 68. The steam passes via 16 and 48 to dilution tank 48.

'I'he phenol necessary tothe production of the phenate in 56 is obtained from the water-phenol layer 55 in separator' 63. This is fed via 68 to a phenate producer 56 which is held at 100 C.

vInto the producer 56 is also charged the remainder of the sodium sulphite separated in the centri- Iuge or illter 52 and discharged via 55, and lime (5 per cent excess over stoichiometric proportions) is likewise fed at 10 from hopper 1I. The phenol reacts with the sodium sulphite and lime in 56 to precipitate the insoluble calcium sulphite and to yield the sodium phenate in solution which is discharged at 12 into a centrifuge 13 which separates the precipitate from the phenate solution. The calcium sulte, previously washed with water to avoid loss of phenol, is discharged at 14 and the latter at 15 to join feed 51, 58 into evaporator 59 and, if desired, to join feed 51, 50 into dilution tank 48.

This step 'has the further advantage that it avoids the extraction of phenol from the phenolic water. 'I'he amount of phenol to be so recycled as phenate via 6| and 36 is about in molar proportion of the benzene reacted, and this proportion can be controlled in the hydrolysis step.

Summary The particularly outstanding improvements provided by the present invention which make continuous operations possible, can be summarized as follows:

I. Essential reduction in the formation of diphenyl-sulfone in the sulfonation step by the presence of sodium benzene sulfonate, or a salt forming the sulfonate, and a two-stage sulfonation of (a) concurrent liquid phase and (b) countercurrent vapor phase;

II. Preparation of the sulfonate by neutralization with sodium sulfite (formed in the system) and without heat-concentration (cooling and centriiuging being substituted), with the consequent avoidance of foaming, or the preferred alternative of neutralization in the dry state by feeding the melted sulfonic acid into solid sodium sulfite.

III. Hydrolysis of a separately fused anhydrous solution of the sodium benzene sulfonate in sodium phenate to yield free phenol and the sodium sulte;

IV. Preparation of the phenate for step III from the water solution of phenol formed in the hydrolysis through the action thereon of a slight excess of lime and of sodium sulfite whereby the by-product iscalcium sulfite and the sodium is retained in the system.

It is to be noted further that the steps are interdependent to the end of providing a continuous process; the two-stage liquid concurrent and vapor counter-current sulfonation of step I and the sulfonate fromstep II as the control provide the monosulfonic acid of necessary high yield and purity for step II; the neutralization step II contributes the acid-forming ingredients of sulfur dioxide and water for step I and in ad- *l l 7 dition the sulfonate for controlling the reaction of step I; the hydrolysis of step III supplies the sodium suli'lte necessary to steps II and IV; and the phenate of step IV is the active ingredient upon which step III hinges, and its concentration supplies the water for the lhydrolysis of step III.

The invention finds its principal utility in the preparation of phenol as set out in the foregoing description. The process, however, is in no essential way altered for preparing other phenols or monohydroxy-aromatic or heterocyclic compounds, such as alkylated hydroxy-benzenes, hydroxynaphthalenes, hydroxy-pyridines, etc., and obtainable from the corresponding mono-sulfonic acids that do not readily decompose or lead to side reactions. Sodium is replaced by potassium and other alkali metals, and calcium can be substituted vby other alkaline earth metals.-

What is claimed is: Process for preparing phenoLwhich comprises feeding concurrently liquid benzene and oleum in substantially molar ratio at a temperature of about 60 to 80 C. for partial conversion into benzene mono-sulfonic acid in the presence of from about 5 to 10 per cent of sodium benzene sulfonate; directing the stream to a separate zone at a temperature of about 150 to 170 C. and passing countercurrently through the mass benzene vapors until a 90 or more per cent monosulfonic acid is formed; neutralizing the sulfonic acid with sodium sulte at about 105 C., cooling and separating the resulting sodium benzene sul- Y fonate; directingthe sulfonate into a mass of melted sodium phenate, discharging the melted mass into a separate zone forV passing therethrough dry steam to hydroiyz'e the melted lmass into free phenol and sodium suiilte and to carry oi the released phenol; retm'ning the sodium 4siilflte to the system; condensing the vapors from the hydrolysis, decanting the water-phenol layer of the condensate and drawing oil the separated free phenol layer; and reacting the water-phenol layer with the sodium sulfite and lime to form, sodium phenate in solution and precipitate calcium sulte; and returning the sodium phenate solution so 'formed for concentration to supply steam and sodium phenate for the hydrolysis. j

VITTORIO MOLINARI.

HERBERT G. .AFFHOLTER..

REFERENCES CITED The following references are of record in the le of this patent-z l UNITED STATES PATENTS Tyrer Sept. 3, 1946 

